Recent progress in the synthesis and characterization of well-defined conjugated polymers and oligomers is presented. The different synthetic schemes for most of the important conjugated polymers will be discussed using a subdivision into three main sections, covering hydrocarbon polymers, heterocyclic polymers and the oligomers, respectively. Although the materials properties will be referred to, the main emphasis of the review is directed to the different strategies that are now available to produce conjugated polymers and well-defined oligomers in a reproducible way and with full control over most of the important macromolecular properties.